This invention relates to a flame retarded thermoplastic composition which is excellent in flame retardancy, heat resistance, light resistance and impact strength.
Thermoplastics have been widely used to fabricate various industrial and household items for their molding capability with ease as well as physical and electrical properties of the molded products. Since most of thermoplastics are inflammable in nature, their use is limited to certain fields unless they are flame retarded.
A variety of flame retardants are known including halogen-containing flame retardants, phosphorous-containing flame retardants, halogen and phosphorous-containing flame retardants and the like. Since thermoplastics have diversified fields of use, it is generally difficult to select a particular flame retardant which would achieve an optimum result in that use. In addition, some of known flame retardants are less compatible with molten thermoplastics, causing bleeding out or darkening of the molded products with time.
Various attempts have been made with limited success to improve these defects by using two or more flame retardants in combination which would compensate for each of their defects. For example, Japanese Laid Open (Kokai) Patent Application No. 79941/1978 discloses a flame retardant system containing a brominated phthalimide. The vrominated phthalimide used, however, has a melting point higher than the molding temperature of most of thermoplastics and, therefore, will not be dispersed uniformly in molten thermoplastics during the molding process. This adversely affects the physical characteristics of molded products significantly.
Japanese Laid Open (Kokai) Patent Application No. 211354/86 discloses a flame retardant system including a bromine-containing epoxy polymer in combination with tetrabromobisphenol A. This system exhibits an improvement in heat resistance, weatherability etc., compared to tetrabromobisphenol A alone. However, the bromine-containing epoxy polymer will not fully react with tetrabromobisphenol A during the molding process and thus the presence of unreacted tetrabromobisphenol A in the molded products can adversely affect the physical characteristics thereof such as heat resistance and weatherability.
It is, therefore, a principal object of the present invention to provide a flame retarded thermoplastic composition which is free from the above disadvantages.
It is another object of the present invention to provide a flame retarded thermoplastic composition having an improved flame retardancy without compromising thermal and mechanical properties of the molded products made therefrom.